1. Field of the Invention
This invention relates to a work locating method for use in an automatic exposing apparatus for forming a photomask on a work such as a printed wiring board, a print board or the like.
2. Description of the Related Art
Two types of locating or positioning systems have been hitherto utilized to perform a locating or positioning operation for a conventional automatic exposing apparatus. One of the locating systems is called an "inside locating system" in which both of an exposing section for irradiating ultraviolet rays and a locating section for performing a locating or positioning operation between a mask film (or glass dry plate) and a work are disposed at the same place, and the other of the locating systems is called as "outside locating system" in which the exposing section and the locating section are disposed at different places.
The applicant of this application has already proposed "outside locating system" as disclosed in Japanese Laid-open No. Hei 1-302259 which corresponds to U.S. Pat. No. 4,996,763 entitled "METHOD OF LOCATING WORK IN AUTOMATIC EXPOSING APPARATUS". This apparatus adopts a work which is beforehand formed with alignment marks, and an automatic aligning device for reading out the alignment marks before the work is fed into an exposing chamber for an exposure process and subjecting the read-out alignment mark to an image processing to locate the work at a predetermined locating position in the exposing chamber on the basis of the processed data. In more detail, the work is fixedly positioned on an alignment table of the automatic aligning device by vacuum-suction of a suction device, and an image-recognizable camera is moved to such a position that alignment marks formed at any positions of various kinds of works can be read out through a transparent window provided at a broad area of the alignment table. Thereafter, on the basis of position information on the moving position of the camera itself and the positions of the alignment marks which are detected by the camera and located in an image receiving area of the camera, the alignment table on which the work is fixedly mounted by the vacuum suction is displaced such that the alignment marks of the work are disposed in correspondence to predetermined positions inside of the exposing chamber.
The "inside locating system" has an advantage that the alignment can be performed with high accuracy because alignment accuracy just before an exposing process is started can be confirmed, but a disadvantage that producibility is low because the aligning and exposing operations are carried out in serial sequence mode. On the other hand, the "outside locating system" has an advantage that the producibility is high because the aligning and exposing operations are carried out in a parallel series mode, but has disadvantages that the alignment accuracy is dependent on mechanical accuracy of a feeding member located between the locating section and the exposing section, that the photomask suffers thermal deformation in the exposing process, and that the alignment accuracy just before the exposing process is started can be hardly confirmed.